SSTO Help

[shrunknuts]

My SSTO reaches 15 - 20 km and 400m/s but then the prograde continuously drops until its below zero and my plane is losing altitude no matter how much I try and pitch it up to correct it. How do i stop it from doing this?

Edited September 11, 2022 by shrunknuts

[Echo__3]

You may want to add a set of canards. It will also be beneficial to increase the angle of incidence on your main wings. With four RAPIERS, you will only need one shock cone intake.  Looking at your mass, you can probably also remove a couple of the RAPIERS. That will help reduce your mass by quite a bit and move your center of mass further forward.

[Lt_Duckweed]

With the amount of wing area you have, you should be going MUCH faster than 400 m/s at 15km.

I typically don't even leave sea level until past 400m/s and by 15km am well over 1000m/s

[mhoram]

Rapiers have the special behavior, that they can not accelerate at high altitudes, if you travel too slow: try to accelerate to 500-600m/s at altitude < 400m before raising altitude to 10km.

If you want to use mods, have a look at https://forum.kerbalspaceprogram.com/index.php?/topic/177302-1123-kerbal-wind-tunnel-1311/ 
This mod indicates approximately, if your vessel is capable of reaching orbit. It also helps you finding approximations for the best ascent paths.

 

 

Edited September 12, 2022 by mhoram

[jimmymcgoochie]

Mk2 parts have very high drag because they’re also considered “wings” and generate lift. To keep drag down, angle your wings by a few degrees so the front (leading) edge is higher than the rear (trailing) edge- this will make the wings generate lift when the fuselage is level and so generating minimal lift.

Rapiers work better the faster you go so build up speed before climbing, you can easily hit 1500m/s in air-breathing mode and then climb to space. Four Rapiers are a bit overkill for a plane that size and you definitely don’t need four shock cones, try two engines and a single shock cone on the nose- switch to the in-line Mk2 cockpit for that- and ditch the wingtip nacelles to save weight and reduce drag.

Canards near the nose might make the plane handle a bit better by giving it more pitch authority and would also balance the increased lift from angling the main wings. Removing two engines would also move the centre of mass forwards though which might mean canards are less useful. You should also look at any parts you don’t absolutely need (the docking port perhaps? and/or swap to an unscrewed design using the Mk2 drone core and a mk2-1.25m adapter instead of a cockpit) and remove them to reduce mass and so increase delta-V; even removing any unnecessary propellants can help, with the NERV running solely on liquid fuel you only need enough oxidiser to boost your way out of the atmosphere and unless you’re docking you don’t need any monopropellant.